Complete java&j2ee


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Complete java&j2ee

  1. 1. JAVAAbstraction: Showing the essential and hiding the non-Essential is known as Abstraction.Encapsulation: The Wrapping up of data and functions into a single unit is known as Encapsulation. Encapsulation is the term given to the process of hiding the implementation details of the object. Once anobject is encapsulated, its implementation details are not immediately accessible any more. Instead they arepackaged and are only indirectly accessed via the interface of the object.Inheritance: is the Process by which the Obj of one class acquires the properties of Obj’s another Class. A reference variable of a Super Class can be assign to any Sub class derived from the Super class. Inheritance is the method of creating the new class based on already existing class , the new classderived is called Sub class which has all the features of existing class and its own, i.e sub class.Adv: Reusability of code , accessibility of variables and methods of the Base class by the Derived class.Polymorphism: The ability to take more that one form, it supports Method Overloading & MethodOverriding.Method overloading: When a method in a class having the same method name with different arguments(diff Parameters or Signatures) is said to be Method Overloading. This is Compile time Polymorphism.oUsing one identifier to refer to multiple items in the same scope.Method Overriding: When a method in a Class having same method name with same arguments is said tobe Method overriding. This is Run time Polymorphism.oProviding a different implementation of a method in a subclass of the class that originally defined themethod. 1. In Over loading there is a relationship between the methods available in the same class ,where as in Overriding there is relationship between the Super class method and Sub class method. 2. Overloading does not block the Inheritance from the Super class , Where as in Overriding blocksInheritance from the Super Class. 3. In Overloading separate methods share the same name, where as in Overriding Sub class methodreplaces the Super Class.4.Overloading must have different method Signatures , Where as Overriding methods must have sameSignatures.Dynamic dispatch: is a mechanism by which a call to Overridden function is resolved at runtime ratherthan at Compile time, and this is how Java implements Run time Polymorphism.Dynamic Binding: Means the code associated with the given procedure call is not known until the time ofcall the call at run time. (it is associated with Inheritance & Polymorphism).Bite code: Is a optimized set of instructions designed to be executed by Java-run time system, which iscalled the Java Virtual machine (JVM), i.e. in its standard form, the JVM is an Interpreter for byte code. JIT- is a compiler for Byte code, The JIT-Complier is part of the JVM, it complies byte code into executable code in real time, piece-by-piece on demand basis. Final classes : String, Integer , Color, Math Abstract class : Generic servlet, Number classovariable:An item of data named by an identifier.Each variable has a type,such as int or Object,andascopeoclass variable :A data item associated with a particular class as a whole--not with particular instances ofthe class. Class variables are defined in class definitions. Also called a static field. See also instance variable.oinstance variable :Any item of data that is associated with a particular object. Each instance of a class hasits own copy of the instance variables defined in the class. Also called a field. See also class variable.olocal variable :A data item known within a block, but inaccessible to code outside the block. For example,any variable defined within a method is a local variable and cant be used outside the method.oclass method :A method that is invoked without reference to a particular object. Class methods affect theclass as a whole, not a particular instance of the class. Also called a static method. also instance method.oinstance method :Any method that is invoked with respect to an instance of a class. Also called simply amethod. See also class method.Java FAQ Files – NarasaReddy 1
  2. 2. Interface: Interfaces can be used to implement the Inheritance relationship between the non-relatedclasses that do not belongs to the same hierarchy, i.e. any Class and any where in hierarchy. UsingInterface, you can specify what a class must do but not how it does.A class can implement more than one Interface.An Interface can extend one or more interfaces, by using the keyword extends.All the data members in the interface are public, static and Final by default.An Interface method can have only Public, default and Abstract modifiers.An Interface is loaded in memory only when it is needed for the first time.A Class, which implements an Interface, needs to provide the implementation of all the methods in thatInterface.If the Implementation for all the methods declared in the Interface are not provided , the class itself has todeclare abstract, other wise the Class will not compile.If a class Implements two interface and both the Intfs have identical method declaration, it is totally valid.If a class implements tow interfaces both have identical method name and argument list, but differentreturn types, the code will not compile.An Interface can’t be instantiated. Intf Are designed to support dynamic method resolution at run time.An interface can not be native, static, synchronize, final, protected or private.The Interface fields can’t be Private or Protected.A Transient variables and Volatile variables can not be members of Interface.The extends keyword should not used after the Implements keyword, the Extends must always come beforethe Implements keyword.A top level Interface can not be declared as static or final.If an Interface species an exception list for a method, then the class implementing the interface need notdeclare the method with the exception list.If an Interface can’t specify an exception list for a method, the class can’t throw an exception.If an Interface does not specify the exception list for a method, he class can not throw any exception list. The general form of Interface is Access interface name { return-type method-name1(parameter-list); type final-varname1=value; }----------------------- Marker Interfaces : Serializable, Clonable, Remote, EventListener, Having 0 methods Java.lang is the Package of all classes and is automatically imported into all Java Program Interfaces: Clonable , Comparable, RunnableAbstract Class: Abstract classes can be used to implement the inheritance relationship between theclasses that belongs same hierarchy.Classes and methods can be declared as abstract.Abstract class can extend only one Class.If a Class is declared as abstract , no instance of that class can be created.If a method is declared as abstract, the sub class gives the implementation of that class.Even if a single method is declared as abstract in a Class , the class itself can be declared as abstract.Abstract class have at least one abstract method and others may be concrete.In abstract Class the keyword abstract must be used for method.Abstract classes have sub classes.Combination of modifiers Final and Abstract is illegal in java.Abstract Class means - Which has more than one abstract method which doesn’t have method body but atleast one of its methods need to be implemented in derived Class.The general form of abstract class is : abstract type name (parameter list); The Number class in the java.lang package represents the abstract concept of numbers. It makes senseto model numbers in a program, but it doesnt make sense to create a generic number object.Difference Between Interfaces And Abstract class ?Java FAQ Files – NarasaReddy 2
  3. 3. oAll the methods declared in the Interface are Abstract, where as abstract class must have atleast one abstract method and others may be concrete. oIn abstract class keyword abstract must be used for method, where as in Interface we need not use the keyword for methods. oAbstract class must have Sub class, where as Interface can’t have sub classes. oAn abstract class can extend only one class, where as an Interface can extend more than one.What are access specifiers and access modifiers ? Accesss specifiers Access modifiers Public Public Protected Abstract Private Final Static Volatile Constant Synchronized Transient Native •Public : The Variables and methods can be access any where and any package. •Protected : The Variables and methods can be access same Class, same Package & sub class. •Private : The variable and methods can be access in same class only. Same class - Public, Protected, and Private Same-package & subclass - Public, Protected Same Package & non-sub classes - Public, Protected Different package & Sub classes - Public, Protected Different package & non- sub classes - Public Identifiers : are the Variables that are declared under particular Datatype. Literals: are the values assigned to the Identifiers. Static : access modifier. Signa: Variable-Static int b; Method- static void meth(int x) When a member is declared as Static, it can be accessed before any objects of its class are created and without reference to any object. Eg : main(),it must call before any object exit. Static can be applied to Inner classes, Variables and Methods. Local variables can’t be declared as static. A static method can access only static Variables. and they can’t refer to this or super in any way. Static methods can’t be abstract. A static method may be called without creating any instance of the class. Only one instance of static variable will exit any amount of class instances. Final : access modifier All the Variables, methods and classes can be declared as Final. Classes declared as final class can’t be sub classed. Method ‘s declared as final can’t be over ridden. If a Variable is declared as final, the value contained in the Variable can’t be changed. Static final variable must be assigned in to a value in static initialized block. Transient : access modifier Transient can be applied only to class level variables. Local variables can’t be declared as transient. During serialization, Object’s transient variables are not serialized. Transient variables may not be final or static. But the complies allows the declaration and no compile time error is generated. Volatile: access modifier Volatile applies to only variables. Volatile can applied to static variables. Java FAQ Files – NarasaReddy 3
  4. 4. Volatile can not be applied to final variables. Transient and volatile can not come together. Volatile is used in multi-processor environments. Native : access modifier Native applies to only to methods. Native can be applied to static methods also. Native methods can not be abstract. Native methods can throw exceptions. Native method is like an abstract method. The implementation of the abstract class and native method exist some where else, other than the class in which the method is declared. Synchronized : access modifier Synchronized keyword can be applied to methods or parts of the methods only. Synchronize keyword is used to control the access to critical code in multi-threaded programming.Declaration of access specifier and access modifiers :Class - Public, Abstract, FinalInner Class - Public, Protected, Private, Final, Static,Anonymous - Public, Protected, Private, StaticVariable - Public, Protected, Private, Final, Static, Transient, Volatile, NativeMethod - Public, Protected, Private, Final, Abstract, Static, Native, SynchronizedConstructor - Public, Protected, PrivateFree-floating code block - Static, Synchronized Package : A Package is a collection of Classes Interfaces that provides a high-level layer of access protection and name space management. Finalize( ) method: All the objects have Finalize() method, this method is inherited from the Object class. Finalize() is used to release the system resources other than memory(such as file handles& network connec’s. Finalize( ) is used just before an object is destroyed and can be called prior to garbage collection. Finalize() is called only once for an Object. If any exception is thrown in the finalize() the object is still eligible for garbage collection. Finalize() can be called explicitly. And can be overloaded, but only original method will be called by Ga- collect. Finalize( ) may only be invoked once by the Garbage Collector when the Object is unreachable. The signature finalize( ) : protected void finalize() throws Throwable { } Constructor( ) : A constructor method is special kind of method that determines how an object is initialized when created. Constructor has the same name as class name. Constructor does not have return type. Constructor cannot be over ridden and can be over loaded. Default constructor is automatically generated by compiler if class does not have once. If explicit constructor is there in the class the default constructor is not generated. If a sub class has a default constructor and super class has explicit constructor the code will not compile. Object : Object is a Super class for all the classes. The methods in Object class as follows. Object clone( ) final void notify( ) Int hashCode( ) Boolean equals( ) final void notify( ) Void finalize( ) String toString( ) Final Class getClass( ) final void wait( ) Class : The Class class is used to represent the classes and interfaces that are loaded by the JAVA Program. Java FAQ Files – NarasaReddy 4
  5. 5. Character : A class whose instances can hold a single character value. This class also defines handymethods that can manipulate or inspect single-character data.constructors and methods provided by the Character class:Character(char) : The Character classs only constructor, which creates a Character object containingthe value provided by the argument. Once a Character object has been created, the value it containscannot be changed.compareTo(Character) :An instance method that compares the values held by two character objects.equals(Object) : An instance method that compares the value held by the current object with thevalue held by another.toString() : An instance method that converts the object to a string.charValue() :An instance method that returns the value held by the character object as a primitivechar value.isUpperCase(char) : A class method that determines whether a primitive char value is uppercase.String: String is Immutable and String Is a final class. The String class provides for strings whose valuewill not change. One accessor method that you can use with both strings and string buffers is the length() method, whichreturns the number of characters contained in the string or the string buffer. The methods in StringClass:-toString( ) equals( ) indexOff( ) LowerCase( )charAt( ) compareTo( ) lastIndexOff( ) UpperCase( )getChars( ) subString( ) trim( )getBytes( ) concat( ) valueOf( )toCharArray( ) replace( )ValueOf( ) : converts data from its internal formate into human readable formate.String Buffer : Is Mutable , The StringBuffer class provides for strings that will be modified; you use stringbuffers when you know that the value of the character data will change. In addition to length, the StringBuffer class has a method called capacity, which returns the amount ofspace allocated for the string buffer rather than the amount of space used.The methods in StringBuffer Class:-length( ) append( ) replace( ) charAt( ) and setCharAt( )capacity( ) insert( ) substring( ) getChars( )ensureCapacity( ) reverse( )setLength( ) delete( )Wraper Classes : are the classes that allow primitive types to be accessed as Objects.These classes are similar to primitive data types but starting with capital letter.Number Byte BooleanDouble Short CharacterFloat Integer Longprimitive Datatypes in Java :According to Java in a Nutshell, 5th ed boolean, byte, char, short, long float, double, int.Float class : The Float and Double provides the methods isInfinite( ) and isNaN( ).isInfinite( ) : returns true if the value being tested is infinetly large or small.isNaN( ) : returns true if the value being tested is not a number.Character class : defines forDigit( ) digit( ) .ForDigit( ) : returns the digit character associated with the value of num.digit( ) : returns the integer value associated with the specified character (which is presumably) accordingto the specified radix.String Tokenizer : provide parsing process in which it identifies the delimiters provided by the user, bydefault delimiters are spaces, tab, new line etc., and separates them from the tokens. Tokens are those whichare separated by delimiters.Observable Class: Objects that subclass the Observable class maintain a list of observers. When anObservable object is updated it invokes the update( ) method of each of its observers to notify the observersthat it has changed state.Java FAQ Files – NarasaReddy 5
  6. 6. Observer interface : is implemented by objects that observe Observable objects.Instanceof( ) :is used to check to see if an object can be cast into a specified type with out throwing acast class exception.IsInstanceof( ) : determines if the specified Object is assignment-compatible with the object representedby this class. This method is dynamic equivalent of the Java language instanceof operator. The methodreturns true if the specified Object argument is non-null and can be cast to the reference type represented bythis Class object without raising a ClassCastException. It returns false otherwise.Garbage Collection : When an object is no longer referred to by any variable, java automatically reclaimsmemory used by that object. This is known as garbage collection.System.gc() method may be used to call it explicitly and does not force the garbage collection but onlysuggests that the JVM may make an effort to do the Garbage Collection.•this() : can be used to invoke a constructor of the same class.•super() :can be used to invoke a super class constructor.Inner class : classes defined in other classes, including those defined in methods are called inner classes.An inner class can have any accessibility including private.Anonymous class : Anonymous class is a class defined inside a method without a name and isinstantiated and declared in the same place and cannot have explicit constructors.What is reflection API? How are they implemented Reflection package is used mainlyfor the purpose of getting the class name. by useing the getName methodwe can get name of the class for particular application. Reflection is a feature of the Java programminglanguage. It allows an executing Java program to examine or "introspect" upon itself, and manipulate internalproperties of the program.What is heap in Java JAVA is fully Object oriented language. It has two phases first one is Compilation phase and second oneis interpratation phase. The Compilation phase convert the java file to class file (byte code is only readableformat of JVM) than Intepratation phase interorate the class file line by line and give the proper result.main( ) : is the method where Java application Begins.String args[ ] : receives any command line argument during runtime.System : is a predefined Class that provides access to the System.Out : is output stream connected to console.Println :displays the output.Downcasting : is the casting from a general to a more specific type, i.e casting down the hierarchy. Doinga cast from a base class to more specific Class, the cast does;t convert the Object, just asserts it actually is amore specific extended Object.Upcasting : byte can take Integer values.Java FAQ Files – NarasaReddy 6
  7. 7. Exception eption handling eption can be generated by Java-runtime system or they can be manually generated by code.Error-Handling becomes a necessary while developing an application to account for exceptional situations that mayur during the program execution, such as Run out of memory Resource allocation Error Inability to find a file Problems in Network connectivity. If the Resource file is not present in the disk, you can use the Exception handling mechanisim to handle such abrupt termination of program. Exception class : is used for the exceptional conditions that are trapped by the program.n exception is an abnormal condition or error that occur during the execution of the program. Error : the error class defines the conditions that do not occur under normal conditions. Run out of memory, Stack overflow error.a.lang.Object….Java.Lang.Throwable Throwable +…. Java.lang.Error +…. A whole bunch of errors Exception Error….Java.Lang.Exception (Unchecked, Checked) +….Java.Lang.RuntimeException | +…. Various Unchecked Exception | +…. Various checked Exceptions. types of exceptions: hecked Exceptions : must be declare in the method declaration or caught in a catch block.hecked exception must be handled at Compile Time. Environmental error that cannot necessarly be detected by ing, Eg: disk full, brocken Socket, Database unavailable etc.Un-checked Exceptions: Run-time Exceptions and Error, does’t have to be declare.(but can be caught). -time Exceptions : programming errors that should be detectd in Testing , hmetic, Null pointer, ArrayIndexOutofBounds, ArrayStore, FilenotFound, NumberFormate, IO, OutofMemory. rs: Virtual mechine error – class not found , out of memory, no such method , illegal access to private field , etc.a Exception handling can be managed by five keywords: Try : The try block governs the statements that are enclosed within it and defines the scope of exception handler associated with it. Try block follows catch or finally or both. Catch: This is a default exception handler. since the exception class is the base class for all the exception class, this handler id capable of catching any type of exception. Java FAQ Files – NarasaReddy 7
  8. 8. The catch statement takes an Object of exception class as a parameter, if an exception is thrown the statement in catch block is executed. The catch block is restricted to the statements in the proceeding try block only. { // statements that may cause exception } h(Exception obj) } Finally : when an exception is raised, the statement in the try block is ignored, some times it is necessary to process certain statements irrespective of wheather an exception is raised or not, the finally block is used for this purpose. Throw : The throw class is used to call exception explicitly. You may want to throw an exception when the user enters a wrong login ID and pass word, you can use throw statement to do so. throw statement takes an single argument, which is an Object of exception class. row<throwable Instance>he Object does not belong to a valid exception class the compiler gives error. Throws :The throws statement species the list of exception that has thrown by a method. If a method is capable of raising an exception that is does not handle, it must specify the exception has to bedle by the calling method, this is done by using the throw statement. [<access specifier>] [<access modifier>] <return type> <method name> <arg-list> [<exception->] Eg: public void accept password( ) throws illegalException { System.out.println(“Intruder”); Throw new illegalAccesException; } Java FAQ Files – NarasaReddy 8
  9. 9. Multi Programming A multithreaded program contains two or more parts that can run concurrently, Each part a program iscalled thread and each part that defines a separate path of excution. Thus multithreading is a specified from of multitasking .There are two distinct types of multitasking .Process: A Process is , in essence , a program that is executing. Process-based :is heavy weight- allows you run two or more programs concurrently.Eg: you can use JAVA compiler at the same time you are using text editor. Here a program is a small unit of code that can be dispatched by scheduler .Thread-based: is Light weight- A Program can perform two or more tasks simultaneously.Creating a thread:Eg: A text editor can formate at the same time you can print, as long as these two tasks are being performseparate treads.Thread: can be defined as single sequential flow of control with in a program.Single Thread : Application can perform only one task at a time.Multithreaded : A process having more than one thread is said to be multithreaded. The multiple threads in the process run at the same time, perform different task and interact with each other. Daemon Thread : Is a low priority thread which runs immedeatly on the back ground doing the Garbage Collection operation for the Java Run time System.SetDaemon( ) – is used to create DaemonThread. Creating a Thread :1. By implementing the Runnable Interface. 2.By extending the thread Class. Thread Class : Java.lang.Threadclass is used to construct and access the individual threads in a multithreaded application.Syntax: Public Class <class name> extends Thread { }The Thread class define several methods . oGetname() – obtain a thread name. oGetname() – obtain thread priority. oStart( ) - start a thread by calling a Run( ). oRun( ) - Entry point for the thread. oSleep( ) - suspend a thread for a period of time. oIsAlive( ) - Determine if a thread is still running. oJoin( ) - wait for a thread to terminate. Runable Interface : The Runnable interface consist of a Single method Run( ), which is executed when the thread is activated. When a program need ti inherit from another class besides the thread Class, you need to implement the Runnable interface. Syntax: public void <Class-name> extends <SuperClass-name> implements Runnable Eg: public Class myapplet extends Japplet implements Runnable { // Implement the Class } * Runnable interface is the most advantageous method to create threads because we need not extend thread Class here. Life Cycle of Thread : Java FAQ Files – NarasaReddy 9 Runnable
  10. 10. New Thread -- ---- Not Runnable ---- Dead The Run( ) terminates . New Thread : When an instance of a thread class is created, a thread enters the new thread state. Thread newThread = new Thread(this); You have to invoke the Start( ) to start the thread. ie, newThread.Start( ); Runnable : when the Start( ) of the thread is invoked the thread enters into the Runnable State. Not Runnable : A thread is said to be not runnable state if it  Is Slleping  Is Waiting  Is being blocked by another thread. sleep(long t); where t= no: of milliseconds for which the thread is inactive. The sleep( ) is a static method because it operates on the current thread. Dead : A thread can either die natuarally or be killed. - A thread dies a natural death when the loop in the Run( ) is complete. - Assigning null to the thread Object kills the thread. - If th loop in the Run( ) has a hundread iterations , the life of the thread is a hundread iterators of the loop. IsAlive( ) : of the thread class is used to determine wheather a thread has been started or stopped. If isAlive( ) returns true the thread is still running otherwise running completed. Thread Priorities : are used by the thread scheduler to decide when each thread should ne allowed to run.To set a thread priority, use te setpriority( ), which is a member of a thread. final void setpriority(int level) - here level specifies the new priority seting for the calling thread. The value level must be with in the range :- MIN_PRIORITY = 1 NORM_PRIORITY = 5 MAX_PRIORITY = 10 You can obtain the current priority setting by calling getpriority( ) of thread. final int getpriority( ) Synchronization : Two ro more threads trying to access the same method at the same point of time leads to synchronization. If that method is declared as Synchronized , only one thread can access it at a time. Another thread can access that method only if the first thread’s task is completed. Synchronized statement : Synchronized statements are similar to Synchronized method. A Synchronized statements can only be executed after a thread has acquired a lock for the object or Classreffered in the Synchronized statements.The general form is - Synchronized(object) { // statements to be Synchronized } Inter Thread Communication : To Avoid pooling , Java includes an elegant interprocess communication mechanisim.Wait( ) - tells the calling thread to give up the monitor and go to sleep until some other thread enters thesame monitor & call notify( ).notify( ) - wake up the first thread that called wait( ) on the same Object.notifyall( ) – wake up all the threads that called wait( ) on the same Object. The highest priority thread aill run fast. Java FAQ Files – NarasaReddy 10
  11. 11. Serialization : The process of writing the state of Object to a byte stream to transfer over the network is known as Serialization. Deserialization : and restored these Objects by deserialization. Externalizable : is an interface that extends Serializable interface and sends data into strems in compressed format. It has two methods WriteExternal(Objectoutput out) ReadExternal(objectInput in)/O Package*;here are two classifications. •ByteStream - console input •CharacterStream – File . ByteStream : Console Input Read( ) - one character Readline( ) – one StringBufferReader br = new BufferReader(new InputStreamReader(;. CharacterStream : File FileInputStream - Store the contents to the File. FileOutStream - Get the contents from File. intWrite pw = new printwriter(System.out.true);Pw.println(“ “);g :- Class myadd { public static void main(String args[ ]) { BufferReader br = new BufferReader(new InputStreamReader(; System.out.println(“Enter A no : “); int a = Integer.parseInt(br.Read( )); System.out.println(“Enter B no : “); int b = Integer.parseInt(br.Read( )); System.out.println(“The Addition is : “ (a+b)); } } Collections Collections : A collection allows a group of objects to be treated as a single unit. collection define a set of core Interfaces as follows. Collection Map Hash Map class Hash Table class Set Hash set List Array List Sorted set Tree set Vector List Java FAQ Files – NarasaReddy 11
  12. 12. Linked List Sorted map Tree Map class Collection Interface : The CI is the root of collection hierarchy and is used for common functionality across all collections. There is no direct implementation of Collection Interface. Set Interface: extends Collection Interface. The Class Hash set implements Set Interface. Is used to represent the group of unique elements. Set stores elements in an unordered way but does not contain duplicate elements. Sorted set : extends Set Interface. The class Tree Set implements Sorted set Interface. It provides the extra functionality of keeping the elements sorted. It represents the collection consisting of Unique, sorted elements in ascending order. List : extends Collection Interface. The classes Array List, Vector List & Linked List implements List Interface. Represents the sequence of numbers in a fixed order. But may contain duplicate elements. Elements can be inserted or retrieved by their position in the List using Zero based index. List stores elements in an ordered way. Map Interface:basic Interface.The classesHash Map & Hash Table implements Map interface. Used to represent the mapping of unique keys to values. By using the key value we can retrive the values. Two basic operations are get( ) & put( ) . Sorted Map : extends Map Interface. The Class Tree Map implements Sorted Map Interface. Maintain the values of key order. The entries are maintained in ascending order. Collection classes: Abstract Collection Abstract List Abstract Set Abstract Map Abstract Array List Hash Set Tree Set Hash Map Tree MapSequential List Linked List List Map | | Abstract List Dictonary | | Vector HashTable | | Stack Properities HashSet : Implements Set Interface. HashSet hs=new HashSet( ); The elements are not stored in sorted order. hs.add(“m”); TreeSet : Implements Sorted set Interface. TreeSet ts=new TreeSet( ); The elements are stored in sorted ascending order. ts.add(“H”); Access and retrieval times are quit fast, when storing a large amount of data. Vector : Implements List Interface. Vector implements dynamic array. Vector v = new vector( ); Vector is a growable object. V1.addElement(new Integer(1)); Vector is Synchronized, it can’t allow special characters and null values. All vector starts with intial capacity, after it is reached next time if we want to store object in vector, the vector automatically allocates space for that Object plus extra room for additional Objects. Java FAQ Files – NarasaReddy 12
  13. 13. ArrayList : Implements List Interface. Array can dynamically increase or decrease size. ArrayList a1=new ArrayList( ); Array List are ment for Random ascessing. A1.add(“a”); Array List are created with intial size, when the size is increased, the collection is automatically enlarged. When an Objects are removed, the array may be shrunk. Linked List : Implements List Interface. Inserting or removing elements in the middle of the array. LinkedList l1=new LinkedList( ); Linked list are meant for Sequential accessing. L1.add(“R”); Stores Objects in a separate link. Map Classes: Abstract Map; Hash Map ; Tree Map Hash Map : Implements Map Interface. Hashmap() , Hashmap(Map m), Hashmap(int capacity) The Elements may not in Order. Hash Map is not synchronized and permits null values Hash Map is not serialized. Hashmap hm = new HashMap( ); Hash Map supports Iterators. hm.put(“Hari”,new Double(11.9)); Hash Table : Implements Map Interface. Hash Table is synchronized and does not permit null values. Hash Table is Serialized. Hashtable ht = new Hashtable( ); Stores key/value pairs in Hash Table. ht.put(“Prasadi”,new Double(74.6)); A Hash Table stores information by using a mechanism called hashing. In hashing the informational content of a key is used to determine a unique value, called its Hash Code. The Hash Code is then used as the index at which the data associated with the key is stored. The Transformation of the key into its Hash Code is performed automatically- we never see the Hash Code. Also the code can’t directly index into h c. Tree Map : Implements Sorted Set Interface. TreeMap tm=new TreeMap( ); The elements are stored in sorted ascending order. tm.put( “Prasad”,new Double(74.6)); Using key value we can retrieve the data. Provides an efficient means of storing key/value pairs in sorted order and allows rapid retrivals. Iterator: Each of collection class provided an iterator( ).By using this iterator Object, we can access each element in the collection – one at a time.We can remove() ; Hashnext( ) – go next; if it returns false –end of list. Iterarator Enumerator Iterator itr = a1.iterator( ); Enumerator vEnum = v.element( ); While(itr.hashNext( )) System.out.println(“Elements in Vector :”); { while(vEnum.hasMoreElements( ) ) Object element = ); System.out.println(vEnum.nextElement( ) + “ “); System.out.println(element + “ “); } Collections 1.Introduction 2.Legacy Collections 1. The Enumeration Interface 2. Vector 3. Stack 4. Hashtable 5. Properties 3.Java 2 Collections 1. The Interfaces of the collections framework 2. Classes in the collections framework 3. ArrayList & HashSet 4. TreeSet & Maps Introduction : •Does your class need a way to easily search through thousands of items quickly? Java FAQ Files – NarasaReddy 13
  14. 14. • Does it need an ordered sequence of elements and the ability to rapidly insert and remove elements in the middle of the sequence?• Does it need an array like structure with random-access ability that can grow at runtime? List Map | | Abstract List Dictonary | | Vector HashTable | | Stack Properities The Enumeration Interface : •enumerate (obtain one at a time) the elements in a collection of objects. specifies two methods : boolean hasMoreElements() : Returns true when there are still more elements to extract, and false when all of the elements have been enumerated. Object nextElement() : Returns the next object in the enumeration as a generic Object reference. VECTOR : Vector implements dynamic array. Vector v = new vector( ); Vector is a growable object. V1.addElement(new Integer(1)); Vector is Synchronized, it can’t allow special characters and null values. Vector is a variable-length array of object references. Vectors are created with an initial size. When this size is exceeded, the vector is automatically enlarged. When objects are removed, the vector may be shrunk. Constructors : Vector() : Default constructor with initial size 10. Vector(int size) : Vector whose initial capacity is specified by size. Vector(int size,int incr) :Vector whose initialize capacity is specified by size and whose increment is specified by incr. Methods : final void addElement(Object element) : The object specified by element is added to the vector. final Object elementAt(int index) : Returns the element at the location specified by index. final boolean removeElement(Object element) : Removes element from the vector final boolean isEmpty() : Returns true if the vector is empty, false otherwise. final int size() : Returns the number of elements currently in the vector. final boolean contains(Object element) : Returns true if element is contained by the vector and false if it is not. STACK : •Stack is a subclass of Vector that implements a standard last-in, first-out stack Constructor : Stack() Creates an empty stack. Methods : Object push(Object item) : Pushes an item onto the top of this stack. Object pop() : Removes the object at the top of this stack and returns that object as the value of this function. An EmptyStackException is thrown if it is called on empty stack. boolean empty() : Tests if this stack is empty. Object peek() : Looks at the object at the top of this stack without removing it from the stack. int search(Object o) : Determine if an object exists on the stack and returns the number of pops that would be required to bring it to the top of the stack. HashTable :Hash Table is synchronized and does not permit null values.Hash Table is Serialized. Hashtable ht = new Hashtable( );Stores key/value pairs in Hash Table. ht.put(“Prasadi”,new Double(74.6)); Hashtable is a concrete implementation of a Dictionary. Java FAQ Files – NarasaReddy 14
  15. 15. Dictionary is an abstract class that represents a key/value storage repository. A Hashtable instance can be used store arbitrary objects which are indexed by any other arbitrary object. A Hashtable stores information using a mechanism called hashing. When using a Hashtable, you specify an object that is used as a key and the value (data) that you want linked to that key. Constructors : Hashtable() Hashtable(int size) Methods : Object put(Object key,Object value) : Inserts a key and a value into the hashtable. Object get(Object key) : Returns the object that contains the value associated with key. boolean contains(Object value) : Returns true if the given value is available in the hashtable. If not, returns false. boolean containsKey(Object key) : Returns true if the given key is available in the hashtable. If not, returns false. Enumeration elements() : Returns an enumeration of the values contained in the hashtable. int size() : Returns the number of entries in the hashtable. Properties •Properties is a subclass of Hashtable • Used to maintain lists of values in which the key is a String and the value is also a String • Constructors Properties() Properties(Properties propDefault) : Creates an object that uses propDefault for its default value. Methods : String getProperty(String key) : Returns the value associated with key. Strng getProperty(String key, String defaultProperty) : Returns the value associated with key. defaultProperty is returned if key is neither in the list nor in the default property list . Enumeration propertyNames() : Returns an enumeration of the keys. This includes those keys found in the default property list. The Interfaces in Collections Framework Collection Map IteratorSet List SortedMap ListIterator |SortedSet Collection : A collection allows a group of objects to be treated as a single unit. The Java collections library forms a framework for collection classes. The CI is the root of collection hierarchy and is used for common functionality across all collections. There is no direct implementation of Collection Interface. Two fundamental interfaces for containers: • Collection boolean add(Object element) : Inserts element into a collection Set Interface: extends Collection Interface. The Class Hash set implements Set Interface. Is used to represent the group of unique elements. Set stores elements in an unordered way but does not contain duplicate elements. Java FAQ Files – NarasaReddy 15
  16. 16. identical to Collection interface, but doesn’t accept duplicates. Sorted set : extends Set Interface. The class Tree Set implements Sorted set Interface. It provides the extra functionality of keeping the elements sorted. It represents the collection consisting of Unique, sorted elements in ascending order. expose the comparison object for sorting. List Interface : ordered collection – Elements are added into a particular position. Represents the sequence of numbers in a fixed order. But may contain duplicate elements. Elements can be inserted or retrieved by their position in the List using Zero based index. List stores elements in an ordered way. Map Interface: Basic Interface.The classes Hash Map & HashTable implements Map interface. Used to represent the mapping of unique keys to values. By using the key value we can retrive the values. Two basic operations are get( ) & put( ) . boolean put(Object key, Object value) : Inserts given value into map with key Object get(Object key) : Reads value for the given key. Tree Map Class: Implements Sorted Set Interface.The elements are stored in sorted ascending order.Using key value we can retrieve the data. Provides an efficient means of storing key/value pairs in sorted order and allows rapid retrivals. TreeMap tm=new TreeMap( ); tm.put( “Prasad”,new Double(74.6)); The Classes in Collections Framework Abstract Collection Abstract List Abstract Set Abstract Map Abstract Array List Hash Set Tree Set Hash Map Tree MapSequential List Linked List ArrayList • Similar to Vector: it encapsulates a dynamically reallocated Object[] array • Why use an ArrayList instead of a Vector? • All methods of the Vector class are synchronized, It is safe to access a Vector object from two threads. • ArrayList methods are not synchronized, use ArrayList in case of no synchronization • Use get and set methods instead of elementAt and setElementAt methods of vector HashSet • Implements a set based on a hashtable • The default constructor constructs a hashtable with 101 buckets and a load factor of 0.75 HashSet(int initialCapacity) HashSet(int initialCapacity,float loadFactor) Java FAQ Files – NarasaReddy 16
  17. 17. loadFactor is a measure of how full the hashtable is allowed to get before its capacity is automatically increased • Use Hashset if you don’t care about the ordering of the elements in the collection TreeSet • Similar to hash set, with one added improvement • A tree set is a sorted collection • Insert elements into the collection in any order, when it is iterated, the values are automatically presented in sorted order • Maps : Two implementations for maps: HashMap hashes the keysThe Elements may not in Order.Hash Map is not synchronized and permits null valuesHash Map is not serialized. Hash Map supports Iterators. TreeMap • uses a total ordering on the keys to organize them in a search tree • The hash or comparison function is applied only to the keys • The values associated with the keys are not hashed or compared. How are memory leaks possible in Java If any object variable is still pointing to some object which is of no use, then JVM will not garbage collect that object and object will remain in memory creating memory leak What are the differences between EJB and Java beans the main difference is Ejb componenets are distributed which means develop once and run anywhere. java beans are not distributed. which means the beans cannot be shared . What would happen if you say this = null this will give a compilation error as follows cannot assign value to final variable this Will there be a performance penalty if you make a method synchronized? If so, can you make any design changes to improve the performance yes.the performance will be down if we use synchronization. one can minimise the penalty by including garbage collection algorithm, which reduces the cost of collecting large numbers of short- lived objects. and also by using Improved thread synchronization for invoking the synchronized methods.the invoking will be faster. How would you implement a thread pool public class ThreadPool extends java.lang.Object implements ThreadPoolInt This class is an generic implementation of a thread pool, which takes the following input a) Size of the pool to be constructed b) Name of the class which implements Runnable (which has a visible default constructor) and constructs a thread pool with active threads that are waiting for activation. once the threads have finished processing they come back and wait once again in the pool. This thread pool engine can be locked i.e. if some internal operation is performed on the pool then it is preferable that the thread engine be locked. Locking ensures that no new threads are issued by the engine. However, the currently executing threads are allowed to continue till they come back to the passivePool How does serialization work Its like FIFO method (first in first out) Java FAQ Files – NarasaReddy 17
  18. 18. How does garbage collection work There are several basic strategies for garbage collection: reference counting, mark-sweep, mark-compact, and copying. In addition, some algorithms can do their job incrementally (the entire heap need notbe collected at once, resulting in shorter collection pauses), and some can run while the user program runs(concurrent collectors). Others must perform an entire collection at once while the user program is suspended(so-called stop-the-world collectors). Finally, there are hybrid collectors, such as the generational collectoremployed by the 1.2 and later JDKs, which use different collection algorithms on different areas of the heap How would you pass a java integer by reference to another functionPassing by reference is impossible in JAVA but Java support the object reference so.Object is the only way to pass the integer by refrence.What is the sweep and paint algorithmThe painting algorithm takes as input a source image and a list of brush sizes. sweep algo is that it computesthe arrangement of n lines in the plane ... a correct algorithm,Can a method be static and synchronizedno a static mettod cant be synchronisedDo multiple inheritance in JavaIts not possible directly. That means this feature is not provided by Java, but it can be achieved with the helpof Interface. By implementing more than one interface.What is data encapsulation? What does it buy you The most common example I can think of is a javabean. Encapsulation may be used by creating get andset methods in a class which are used to access the fields of the object. Typically the fields are made privatewhile the get and set methods are public. dEncapsulation can be used to validate the data that is to be stored, to do calculations on data that isstored in a field or fields, or for use in introspection (often the case when using javabeans in Struts, forinstance).What is reflection API? How are they implemented Reflection package is used mainlyfor the purpose of getting the class name. by using the getName methodwe can get name of the class for particular application . Reflection is a feature of the Java programming language. It allows an executing Java program toexamine or "introspect" upon itself, and manipulate internal properties of the program.What are the primitive types in JavaAccording to Java in a Nutshell, 5th edboolean, byte, char, short, long float, double, intIs there a separate stack for each thread in JavaNoWhat is heap in Java JAVA is fully Object oriented language. It has two phases first one is Compilation phase and second oneis interpratation phase. The Compilation phase convert the java file to class file (byte code is only readableformat of JVM) than Intepratation phase interorate the class file line by line and give the proper result.In Java, how are objects / values passed aroundIn Java Object are passed by reference and Primitive data is always pass by valueDo primitive types have a class representationPrimitive data type has a wrapper class to present.Like for int - Integer , for byte Byte, for long Long etc ...How all can you free memoryWith the help of finalize() method.If a programmer really wants to explicitly request a garbage collection at some point, System.gc() orRuntime.gc() can be invoked, which will fire off a garbage collection at that time.Does java do reference counting It is more likely that the JVMs you encounter in the real world will use a tracing algorithm in their garbage-collected heapsWhat does a static inner class mean? How is it different from any other static memberJava FAQ Files – NarasaReddy 18
  19. 19. A static inner class behaves like any ``outer class. It may contain methods and fields. It is not necessarily the case that an instance of the outer class exists even when we have created aninstance of the inner class. Similarly, instantiating the outer class does not create any instances of the innerclass. The methods of a static inner class may access all the members (fields or methods) of the inner classbut they can access only static members (fields or methods) of the outer class. Thus, f can access the field x,but it cannot access the field y.How do you declare constant values in javaUsing Final keyword we can declare the constant values How all can you instantiate final members Finalmember can be instantiate only at the time of declaration. nullHow is serialization implemented in Java A particular class has to implement an Interface for implementing serialization. Whenyou have an object passed to a method and when the object is reassigned to a different one, then is theoriginal reference lost No Reference is not lost. Java always passes the object by reference, now tworeferences is pointing to the same object.What are the different kinds of exceptions? How do you catch a Runtime exceptionThere are 2 types of exceptions.1. Checked exception2. Unchecked exception. Checked exception is catched at the compile time while unchecked exception is checked at run time.1.Checked Exceptions : Environmental error that cannot necessarily be detected by testing; e.g. disk full,broken socket, database unavailable, etc.2. Unchecked exception.Errors : Virtual machine error: class not found, out of memory, no such method, illegal access to private field,etc.Runtime Exceptions :Programming errors that should be detected in testing: index out of bounds, nullpointer, illegal argument, etc.Checked exceptions must be handled at compile time. Runtime exceptions do not need to be. Errors oftencannot beWhat are the differences between JIT and HotSpot The Hotspot VM is a collection of techniques, the most significant of which is called "adaptiveoptimization.The original JVMs interpreted bytecodes one at a time. Second-generation JVMs added a JIT compiler, whichcompiles each method to native code upon first execution, then executes the native code. Thereafter,whenever the method is called, the native code is executed. The adaptive optimization technique used byHotspot is a hybrid approach, one that combines bytecode interpretation and run-time compilation to nativecode.Hotspot, unlike a regular JIT compiling VM, doesnt do "premature optimization"What is a memory footprint? How can you specify the lower and upper limits of the RAM used bythe JVM? What happens when the JVM needs more memory? when JVM needs more memory then it does the garbage collection, and sweeps all the memory which isnot being used.What are the disadvantages of reference counting in garbage collection? An advantage of this scheme is that it can run in small chunks of time closely interwoven with theexecution of the program. This characteristic makes it particularly suitable for real-time environments wherethe program cant be interrupted for very long. A disadvantage of reference counting is that it does not detectcycles. A cycle is two or more objects that refer to one another, for example, a parent object that has areference to its child object, which has a reference back to its parent. These objects will never have areference count of zero even though they may be unreachable by the roots of the executing program.Another disadvantage is the overhead of incrementing and decrementing the reference count each time.Because of these disadvantages, reference counting currently is out of favor.Is it advisable to depend on finalize for all cleanups The purpose of finalization is to give an opportunity to an unreachable object to perform any clean upbefore the object is garbage collected, and it is advisable.Java FAQ Files – NarasaReddy 19
  20. 20. can we declare multiple main() methods in multiple classes. ie can we have each main method inits class in our program?YES JDBCHow to Interact with DB? Generally every DB vendor provides a User Interface through which we can easily execute SQLquery’s and get the result (For example Oracle Query Manager for Oracle, and TOAD ( toolcommon to all the databases). And these tools will help DB developers to create database. But as aprogrammer we want to interact with the DB dynamically to execute some SQL queries from our application(Any application like C, C++, JAVA etc), and for this requirement DB vendors provide some Native Libraries(Vendor Specific) using this we can interact with the DB i.e. If you want to execute some queries on OracleDB, oracle vendor provides an OCI (Oracle Call Interface) Libraries to perform the same.About ODBCWhat is ODBC ODBC (Open Database Connectivity) is an ISV (Independent software vendor product) composes of nativeAPI to connect to different databases through via a single API called ODBC.Open Database Connectivity (ODBC) is an SQL oriented application programming interface developed by incollaboration with IBM and some other database vendors.ODBC comes with Microsoft products and with all databases on Windows OS.ODBC Architecture Oracle ODBC SP API Oracle Front End SQL server SP API SQL Application ODBC API ODBC server “C” function Sybase ODBC SP API Sybase calls Oracle DSN Oracle ODBC Oracle My DSN SQL Server DSN SQL server ODBC SQL Sybase DSN Sybase Sybase ODBC Our DSNAdvantages•Single API (Protocol) is used to interact with any DB•Switching from one DB to another is easy•Doesn’t require any modifications in the Application when you want to shift from one DB to other.What for JDBC? As we have studied about ODBC and is advantages and came to know that it provides a common API tointeract with any DB which has an ODBC Service Provider’s Implementation written in Native API that can beused in your applications.Java FAQ Files – NarasaReddy 20
  21. 21. If an application wants to interact with the DB then the options which have been explained up to now in thisbook are:1.Using Native Libraries given by the DB vendor2.Using ODBC APIAnd we have listed there Advantages and Disadvantages. But if the application is a JAVA application then the above given options are not recommended to be useddue to the following reasons1.Native Libraries given by DB vendora.Application becomes vendor dependent andb.The application has to use JNI to interact with Native Lib which may cause serious problem for PlatformIndependency in our applications.2.And the second option given was using ODBC API which can solve the 1.a problem but again this ODBC APIis also a Native API, so we have to use JNI in our Java applications which lead to the 1.b described problem.And the answer for these problems is JDBC (Java Data Base Connectivity) which provides a common JavaAPI to interact with any DB.What is JDBC As explained above JDBC standards for Java Data Base Connectivity. It is a specification given by SunMicrosystems and standards followed by X/Open SAG (SQL Access Group) CLI (Call Level Interface) tointeract with the DB.Java programing language methods. The JDBC API provides database-independent connectivity between theJAVA Applications and a wide range of tabular data bases. JDBC technology allows an application componentprovider to: •Perform connection and authentication to a database server •Manage transactions •Moves SQL statements to a database engine for preprocessing and execution •Executes stored procedures •Inspects and modifies the results from SELECT statementsJDBC APIJDBC API is divided into two parts1.JDBC Core API2.JDBC Extension or Optional API JDBC Core API (java.sql package) This part of API deals with the following futures1.Establish a connection to a DB2.Getting DB Details3.Getting Driver Details4.maintaining Local Transaction5.executing query’s6.getting result’s (ResultSet)7.preparing pre-compiled SQL query’s and executing8.executing procedures & functions JDBC Ext OR Optional API (javax.sql package) This part of API deals with the following futures1.Resource Objects with Distributed Transaction Management support2.Connection Pooling. These two parts of Specification are the part of J2SE and are inherited into J2EE i.e. this specification API can be used with all the component’s given under J2SE and J2EE. JDBC Architecture: JDBC Application JDB C SP AP JDBC Driver I S S P A P PI A Oracle DB PI MS SQL Sybase DB Server DBJava FAQ Files – NarasaReddy 21
  22. 22. In the above show archetecture diagram the JDBC Driver forms an abstraction layer between theJAVA Application and DB, and is implemented by 3rd party vendors or a DB Vendor. But whoever may be thevendor and what ever may be the DB we need not to worry will just us JDCB API to give instructions to JDBCDriver and then it’s the responsibility of JDBC Driver Provider to convert the JDBC Call to the DB Specific Call.And this 3rd party vendor or DB vendor implemented Drivers are classified into 4-Types namelyTypes Of Drivers :1.Type-1 (JDBC ODBC-Bridge Driver) JDBC-ODBC Bridge Driver2.Type-2 (Java-Native API Driver) Native API Partly JAVA Driver (Thick Driver)3.Type-3 (Java Net Protocol Driver) Intermediate DataBase Access Server4.Type-4 (Java Native Protocol driver) Pure JAVA Driver (Thin driver)Type-1 : JDBC-ODBC Bridge Driver : Since ODBC is written in C-language using pointers, so JAVA does’t support pointers, ajava program can’t communate directly with the DataBase. The JDBC-ODBC bridge drivertransulates JDBCAPI calls to ODBC API calls.Architecture JAVA JDBC Native DBMS Application ODBC ODBC Interface Driver Client client driver libraries Libraries DBMS Interface DBMS Server LibrariesThis type of Driver is designed to convert the JDBC request call to ODBC call and ODBC response call to JDBCcall. The JDBC uses this interface in order to communicate with the database, so neither the database northe middle tier need to be Java compliant. However ODBC binary code must be installed on each clientmachine that uses this driver. This bridge driver uses a configured data source.Advantages•Simple to use because ODBC drivers comes with DB installation/Microsoft front/back office productinstallation•JDBC ODBC Drivers comes with JDK softwareDisadvantages•More number of layers between the application and DB. And more number of API conversions leads to thedownfall of the performance.•Slower than type-2 driverWhere to use? This type of drivers are generaly used at the development time to test your application’s.Because of the disadvantages listed above it is not used at production time. But if we are not available withany other type of driver implementations for a DB then we are forced to use this type of driver (for exampleMicrosoft Access).Examples of this type of driversJdbcOdbcDriver from sunSun’s JdbcOdbcDriver is one of type-1 drivers and comes along with sun j2sdk (JDK).Setting environment to use this driver1.SoftwareODBC libraries has to be installed.Java FAQ Files – NarasaReddy 22
  23. 23. 2.classpathNo additional classpath settings are required apart from the runtime jar (c:j2sdk1.4jrelibrt.jar) which isdefaultly configured.3.PathNo additional path configuration is required.How to use this driver1.Driver class name  sun.jdbc.odbc.JdbcOdbcDriver2.Driver URL  dbc:odbc:<DSN>here <DSN> (Data Source Name) is an ODBC datasource name which is used by ODBC driver to locate oneof the ODBC Service Provider implementation API which can in-turn connect to DB. Steps to create <DSN> ‘Data Sources (ODBC)’ from Control PanalAdministrative Tools(for Windows 2000 server/2000 professional/XP)run ‘ODBC Data Sources’ from Control Panel2. click on Add button available on the above displayed screen. this opens a new window titled ‘Create NewData Source’ which displays all the available DB’s lable DB’s ODBC drivers currently installed on yoursystem.3. Select the suitable driver and click on Finish4. Give the required info to the driver (like username, service id etc)Type-2 : Native API Partly JAVA Driver (Thick Driver) : JDBC Database calls are translated into Vendor-specific API calls. The database willprocess the request and send the results back through API to JDBC Driver – this will translate the results tothe JDBC standard and return them to the Java application. The Vendor specific language API must be installed on every client that runs the JAVA application.Architecture JDBC JDBC Type II DBMS Client Application JDBC Driver SP API libraries (native) SP N/ W DBMS DBMS Server OCI libraries (native)This driver converts the JDBC call given by the Java application to a DB specific native call (i.e. to C or C++)using JNI (Java Native Interface).Advantages :Faster than the other types of drivers due to native library participation in socket programing.Disadvantage : DB spcifiic native client library has to be installed in the client machine.•Preferablly work in local network environment because network service name must be configured in clientsystemWhere to use? This type of drivers are suitable to be used in server side applications. Not recommended to use with the applications using two tire model (i.e. client and database layer’s) becausein this type of model client used to interact with DB using the driver and in such a situation the client systemsould have the DB native library.Examples of this type of drivers1. OCI 8 (Oracle Call Interface) for Oracle implemented by Oracle Corporation.Setting environment to use this driver•Software: Oracle client software has to be installed in client machine•classpath •path  %ORACLE_HOME%ora81binHow to use this driver•Driver class name  oracle.jdbc.driver.OracleDriver•Driver URL  jdbc:oracle:oci8:@TNSNameJava FAQ Files – NarasaReddy 23
  24. 24. Note: TNS Names of Oracle is available in Oracle installed folder %ORACLE_HOME %Ora81networkadmintnsnames.ora2. Weblogic Jdriver for Oracle implemented by BEA Weblogic:Setting environment to use this driver•Oracle client software has to be installed in client machine•weblogicoic dll’s has to be set in the path•classpath  d:beaweblogic700serverlibweblogic.jar•path  %ORACLE_HOME%ora81bin; d:beaweblogic700serverbin<subfolder><sub folder> isooci817_8 if you are using Oracle 8.1.xooci901_8 for Oracle 9.0.xooci920_8 for Oracle 9.2.xHow to use this driver•Driver class name  weblogic.jdbc.oci.Driver•Driver URL  jdbc:weblogic:oracle:HostNameType-3 Intermediate DataBase Access Server : Type-3 Driver uses an Intermediate(middleware) database driver that has the ability toconnect multiple JAVA clients to multiple database servers. Client connect to the Databse server via an Intermediate server component (such as listener) that acts as agateway for multple database servers. Bea weblogic includes Type-3 Driver.Architecture : JDBC JDBC Type III Middleware JDBC Net protocol Application Driver Listener DBMS DBMS Interface DBMS Interface DBMS API OCI Libraries Server Client This type of drivers responsibility is to convert JDBC call to Net protocol (Middleware listenerdependent) format and redirect the client request to Middleware Listener and middleware listener inturn usestype-1, type-2 or type-4 driver to interact with DB.Advantages:•It allows the flexibility on the architecture of the application.•In absence of DB vendor supplied driver we can use this driver•Suitable for Applet clients to connect DB, because it uses Java libraries for communication between clientand server.Disadvantages:•From client to server communication this driver uses Java libraries, but from server to DB connectivity thisdriver uses native libraries, hence number of API conversion and layer of interactions increases to performoperations that leads to performance deficit.•Third party vendor dependent and this driver may not provide suitable driver for all DBsWhere to use?•Suitable for Applets when connecting to databasesExamples of this type of drivers:1. IDS Server (Intersolv) driver available for most of the DatabasesSetting environment to use this driver•Software: IDS software required to be downloaded from the following URL [ -> Export Evaluation ]•classpath  C:IDSServerclassesjdk14drv.jar•path How to use this driver•Driver class name  ids.sql.IDSDriverJava FAQ Files – NarasaReddy 24
  25. 25. •Driver URL  jdbc:ids://localhost:12/conn?dsn=IDSExamples Note: DSN Name must be created in ServerDSNType-4 Pure JAVA Driver (Thin driver) : Type-4 Driver translates JDBC-API calls to direct network calls using vendor specificnetworking protocols by making direct server connections with the database.Architecture JDBC JDBC Type IV DBMS Interface Application JDBC Native Protocol Server Listener Driver DBMS API DBMSThis type of driver converts the JDBC call to a DB defined native protocol.Advantage•Type-4 driver are simple to deploy since there is No client native libraries required to be installed in clientmachine•Comes with most of the DatabasesDisadvantages:•Slower in execution compared with other JDBC Driver due to Java libraries are used in socket communicationwith the DBWhere to use?•This type of drivers are sutable to be used with server side applications, client side application and JavaApplets also.Examples of this type of drivers1) Thin driver for Oracle implemented by Oracle CorporationSetting environment to use this driver•classpath  %ORACLE_HOME%ora81jdbclibclasses111.zipHow to use this driver•Driver class name  oracle.jdbc.driver.OracleDriver•Driver URL  jdbc:oracle:thin:@HostName:<port no>:<SID> <port no>  1521 <SID> -> ORCL2) MySQL Jconnector for MySQL databaseSetting environment to use this driver•classpath  C:mysqlmysql-connector-java-3.0.8-stablemysql-connector-java-3.0.8-stable-bin.jarHow to use this driver•Driver class name  com.mysql.jdbc.Driver•Driver URL  jdbc:mysql:///testChapter 3 [JDBC Core API]In this chapter we are going to discuss about 3 versions of JDBC: JDBC 1.0, 2.0 and 3.0Q) How JDBC API is common to all the Databases and also to all drivers?A) Fine! The answer is JDBC API uses Factory Method and Abstract Factory Design pattern implementations tomake API common to all the Databases and Drivers. In fact most of the classes available in JDBC API areinterfaces, where Driver vendors must provide implementation for the above said interfaces.Q) Then how JDBC developer can remember or find out the syntaxes of vendor specific classes?Java FAQ Files – NarasaReddy 25
  26. 26. A) No! developer need not have to find out the syntaxes of vendor specific implementations why becauseDriverManager is one named class available in JDBC API into which if you register Driver class name, URL,user and password, DriverManager class in-turn brings us one Connection object.Q) Why most of the classes given in JDBC API are interfaces?A) Why abstract class and abstract methods are?Abstract class forces all sub classes to implement common methods whichever are required implementations.Only abstract method and class can do this job. That’s’ why most part of the JDBC API is a formation ofinterfaces.JDBC API comes in 2 packagesjava.sql.*javax.sql.*First of all I want to discuss briefly about all the list of interfaces and classes available in java.sql. packageInterfaces indexDriverEvery JDBC Driver vendor must one sub class of this class for initial establishment of Connections.DriverManager class need to be first registered with this class before accepting URL and other information forgetting DB connection.Method index•Connection connect(String url, Properties info)This method takes URL argument and user name & password info as Properties object•boolean acceptURL(String url)This method returns boolean value true if the given URL is correct, false if any wrong in URL•boolean jdbcComplaint()JDBC compliance requires full support for the JDBC API and full support for SQL 92 Entry Level. It is expectedthat JDBC compliant drivers will be available for all the major commercial databases.Connection Connection is class in-turn holds the TCP/IP connection with DB. Functions available in this class areused to manage connection live-ness as long as JDBC application wants to connect with DB. The period forhow long the connection exists is called as Session. This class also provides functions to execute various SQLstatements on the DB. For instance the operations for DB are mainly divided into 3 types•DDL (create, alter, and drop)•DML (insert, select, update and delete)•DCL (commit, rollback) and also•call function_name (or) call procedure_nameMethod Index•Statement createStatement()•PreparedStatement prepareStatement(String preSqlOperation)•CallableStatement prepareCall(String callToProc())Statement Statement class is the super class in its hierarchy. Provides basic functions to execute query (select) andnon-related (create, alter, drop, insert, update, delete) query operations. Method Index•int executeUpdate(String sql)This function accepts non-query based SQL operations; the return value int tells that how many number ofrows effected/updated by the given SQL operation.•ResultSet executeQuery(String sql)This function accepts SQL statement SELECT and returns java buffer object which contains temporaryinstance of SQL structure maintaining all the records retrieved from the DB. This object exists as long as DBconnection exist.•boolean execute()This function accepts all SQL operations including SELECT statement also.PreparedStatement PreparedStatement class is sub classing from Statement class. While connection class prepareStatementfunction is creating one new instance this class, function takes one String argument that contains basicsyntax of SQL operation represented with “?” for IN parameter representation. In the further stages of theJDBC program, programmer uses setXXX(int index, datatype identifier) to pass values into IN parameter andrequests exdcute()/ exuecteUpdate() call.Method IndexJava FAQ Files – NarasaReddy 26
  27. 27. •setInt(int index, int value) – similar functions are provided for all other primitive parameters•setString(int index, String value)•setObject(int index, Object value)•setBinaryStream(int index, InputStream is, int length)CallableStatementResultSet ResultSetMetaData DatabaseMetaDataBLOB CLOB REFSavePoint StructSQLInput SQLOutput SQLData Class diagram required here// TypeI DriverTest,javapackage com.digitalbook.j2ee.jdbc;import java.sql.*;public class TypeIDriverTest{ Connection con; Statement stmt; ResultSet rs; public TypeIDriverTest () { try { // Load driver class into default ClassLoader Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver"); // Obtain a connection with the loaded driver con =DriverManager.getConnection ("jdbc:odbc:digitalbook","scott","tiger"); URL String - ("<protocol>:<subprotocol>:<subname>", " ", " " ); } // create a statement st=con.createStatement(); //execute SQL query rs =st.executeQuery ("select ename,sal from emp"); System.out.println ("Name Salary"); System.out.println ("--------------------------------"); while( { System.out.println (rs.getString(1)+" "+rs.getString(2)); } rs.close (); stmt.close (); con.close (); } catch(Exception e) { e.printStackTrace (); } } public static void main (String args[]) { TypeIDriverTest demo=new TypeIDriverTest (); } }// TypeIIDriverTest,javapackage com.digitalbook.j2ee.jdbc;import java.sql.*;public class TypeIIDriverTest{ Connection con; Statement stmt; ResultSet rs; public TypeIIDriverTest ()Java FAQ Files – NarasaReddy 27
  28. 28. { try { // Load driver class into default ClassLoader Class.forName ("oracle.jdbc.driver.OracleDriver"); // Obtain a connection with the loaded drivercon =DriverManager.getConnection ("jdbc:oracle:oci8:@digital","scott","tiger"); // create a statement st=con.createStatement(); //execute SQL query rs =st.executeQuery ("select ename,sal from emp"); System.out.println ("Name Salary"); System.out.println ("--------------------------------"); while( { System.out.println (rs.getString(1)+" "+rs.getString(2)); } rs.close (); stmt.close (); con.close (); } catch(Exception e) { e.printStackTrace (); } } public static void main (String args[]) { TypeIIDriverTest demo=new TypeIIDriverTest (); } }Chapter 9 : [javax.sql package]This package supplements the java.sql package and is included as a part of JDK 1.4 version. This packagemainly provides following features:1.DataSource interface was introduced in substitution to DriverManager class for getting connection objects.2.Connection Pooling 3.Distributed TX management 4.RowSets Applications can directly use DataSource and RowSet API but connection pooling and Distributed TXmanagement APIs are used internally by the middle-tier infrastructure.DataSource DataSource is an interface. Driver vendor will provide implementation for this interface (That means incase JDBC Driver Type II driver Oracle vendor for Oracle DB, Intersolv in case of IDSServer). This object isused to obtain connections into any type of JDBC program. Though DriverManager class is ideal for gettingDB connection object, this class provides some extra features over DriverManager class:•Applications will obtain DB connection objects through via this factory class•DataSource object will be registered into JNDI, hence any application connected in the network can obtainthis object by requesting JNDI API, DataSource class is having one method called getConnection() geives oneConnection object•Application do not need to hard code a driver class•Changes can be made to a data source properties, which means that it is not necessary to make changes inapplication code when something about the data source or driver changes•Connection pooling and Distributed transactions are available through only the connection obtained from thisobject. Connection obtained through DriverManager class do not have this capabilityDataSource interface is implemented by driver vendor. There are 3 types of implementations available:1.Basic Implementation- Produces a standard connection object.2.Connection Pooling Implementation- Produces a connection object that automatically participates inconnection pooling. This implementation works with a middle-tier connection pooling manager.Java FAQ Files – NarasaReddy 28
  29. 29. 3.Distributed transaction implementation- Produces a connection object that may be used fordistributed transactions and almost always participates in connection pooling. This implementation works witha middle-tier transaction manager and almost always with a connection pool manager.A driver that is accessed via a DataSource object does not register itself with the DriverManager. Rather, aDataSource object is retrieved though a lookup operation and then used to create a Connection object. With abasic implementation, the connection obtained through a DataSource object is identical to a connectionobtained through the DriverManager facility.Method Index•Connection getConnection() – This function returns Connection object on demand of this method.•Connection getConnection(String user, String pass) – This function returns Connection object on demand ofthis method by passing username and password.Sub classes of this interface areType III Driver – IDSServer – Intersolv – ids.jdbc.IDSDataSourceType III Driver – WebLogic – BEA – weblogic.jdbc.jta.DataSource – XA SupportConnection Pooling Connections made via a DataSource object that is implemented to work with a middle tier connectionpool manager will participate in connection pooling. This can improve the performance dramatically becausecreating a new connection is very expensive.Connection Pool provides following features:•Substantial improvement in the performance of DB application can be accomplished by pre-caching the DBconnection objects•CPM supplied DB connections are remote enable•CPM supplied DB connections are cluster aware•CPM supplied DB connections supports DTM (distributed TXs)•CPM supplied DB connections are not actual DB Connection objects, in turn they are remote object, henceeven though client closes DB connection using con.close() the actual connection may not be closed insteadRMI connection between client to CPM are closed•CPM supplied DB connection objects are serializable, hence client from any where in the network can accessDB connectionsThe classes and interfaces used for connection pooling are:1.ConnectionPoolDataSource2.PooledConnection3.ConnectionEvent4.ConnectionEventListener Connection Pool Manager resided on middle tier system uses these classes and interfaces behind thescenes. When the ConnectionPooledDataSource object is called on to create PooledConnection object, theconnection pool manager will register as a ConnectionEventListener object with the new PooledConnectionobject. When the connection is closed or there is an error, the connection pool manager (being listener) getsa notification that includes a ConnectionEvent object.Distributed Transactions As with pooled connections, connections made via data source object that is implemented to work withthe middle tier infrastructure may participate in distributed transactions. This gives an application the abilityto involve data sources on multiple servers in a single transaction.The classes and interfaces used for distributed transactions are:•XADataSource•XAConnectionThese interfaces are used by transaction manager; an application does not use them directly. The XAConnection interface is derived from the PooledConnection interface, so what applies to a pooledconnection also applies to a connection that is part of distributed transaction. A transaction manager in themiddle tier handles everything transparently. The only change in application code is that an applicationcannot do anything that would interfere with the transaction manager’s handling of the transaction.Specifically application cannot call the methods Connection.commit or Connection.rollback and it cannot setthe connection to be in auto-commit mode. An application does not need to do anything special to participate in a distributed transaction. It simplycreates connections to the data sources it wants to use via the DataSource.getConnection method, just as itnormally does. The transaction manager manages the transaction behind the scenes. The XADataSourceinterface creates XAConnection objects, and each XAConnection object creates an XAResource object that thetransaction manager uses to manage the connection.Java FAQ Files – NarasaReddy 29
  30. 30. Rowsets The RowSet interface works with various other classes and interfaces behind the scenes. These can begrouped into three categories.1.Event NotificationoRowSetListenerA RowSet object is a JavaBeansTM component because it has properties and participates in the JavaBeansevent notification mechanism. The RowSetListener interface is implemented by a component that wants to benotified about events that occur to a particular RowSet object. Such a component registers itself as a listenerwith a rowset via the RowSet.addRowSetListener method.oWhen the RowSet object changes one of its rows, changes all of it rows, or moves its cursor, it also notifieseach listener that is registered with it. The listener reacts by carrying out its implementation of thenotification method called on it.oRowSetEventAs part of its internal notification process, a RowSet object creates an instance of RowSetEvent and passes itto the listener. The listener can use this RowSetEvent object to find out which rowset had the event.2.MetadataRowSetMetaDataThis interface, derived from the ResultSetMetaData interface, provides information about the columns in aRowSet object. An application can use RowSetMetaData methods to find out how many columns the rowsetcontains and what kind of data each column can contain.The RowSetMetaData interface provides methods for setting the information about columns, but anapplication would not normally use these methods. When an application calls the RowSet method execute,the RowSet object will contain a new set of rows, and its RowSetMetaData object will have been internallyupdated to contain information about the new columns.3.The Reader/Writer Facility A RowSet object that implements the RowSetInternal interface can call on the RowSetReader object associated with it to populate itself with data. It can also call on the RowSetWriter object associated with it to write any changes to its rows back to the data source from which it originally got the rows. A rowset that remains connected to its data source does not need to use a reader and writer because it can simply operate on the data source directly.RowSetInternalBy implementing the RowSetInternal interface, a RowSet object gets access to its internal state and is able tocall on its reader and writer. A rowset keeps track of the values in its current rows and of the values thatimmediately preceded the current ones, referred to as the original values. A rowset also keeps track of (1)the parameters that have been set for its command and (2) the connection that was passed to it, if any. Arowset uses the RowSetInternal methods behind the scenes to get access to this information. An applicationdoes not normally invoke these methods directly.RowSetReaderA disconnected RowSet object that has implemented the RowSetInternal interface can call on its reader (theRowSetReader object associated with it) to populate it with data. When an application calls theRowSet.execute method, that method calls on the rowsets reader to do much of the work. Implementationscan vary widely, but generally a reader makes a connection to the data source, reads data from the datasource and populates the rowset with it, and closes the connection. A reader may also update theRowSetMetaData object for its rowset. The rowsets internal state is also updated, either by the reader ordirectly by the method RowSet.execute.RowSetWriterA disconnected RowSet object that has implemented the RowSetInternal interface can call on its writer (theRowSetWriter object associated with it) to write changes back to the underlying data source.Implementations may vary widely, but generally, a writer will do the following:Make a connection to the data sourceCheck to see whether there is a conflict, that is, whether a value that has been changed in the rowset hasalso been changed in the data sourceWrite the new values to the data source if there is no conflictClose the connectionThe RowSet interface may be implemented in any number of ways, and anyone may write an implementation.Developers are encouraged to use their imaginations in coming up with new ways to use rowsets.Java FAQ Files – NarasaReddy 30